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This Diploma-Thesis was made within the GERDA-Experiment. GERDAs aim is to detect the neutrinoless double beta decay of 76Ge. Its detection would prove that neutrinos are Majorana particles. GERDA is still under construction, data acquisition will start in 2008. If neutrinoless double beta events are detected, than we have the half life of double beta decay and the effective neutrino mass. If no double beta event is detected than we have an new lower limit of the half life of the double beta decay (T1/2 > 2 1026 a) und a new upper limit for the effective neutrino mass (mee=0,09-0,29 eV). The assumption to find such a rare neutrinoless double beta decay is to reduce the background by 2-3 orders of magnitude below the current state-of-the-art. A part of the background originates from cosmic rays, this is way GERDA is built underground in the Gran Sasso laboratory. An another part comes from radioactive isotops contained in the building materials, e.g.226Ra which decays to 222Rn. All used gases in GERDA like nitrogen and argon contain radon. My task at the MPIK in Heidelberg was to test and develop a new Lucas cell. Lucas cells are radon detectors which offer the opportunity of online-monitoring of radon in gas. This new lucas cell should be used in GERDA for radon-monitoring in air or gases like nitrogen (argon) in clean rooms and clean benches, because the atmosphere should content low radon (e.g. to minimize the contamination of the germanium crystalls). Because of the high purity standarts for GERDA, a Lucas cell with a much better sensitivity compared to normally used ones should be constructed. To achieve this, I tried a plastic foil (because of its purity) which is normaly used as wavelength shifter and reflector if it could be used as a scintillator.
